1. Field of the Invention
The present invention relates to process control systems and methods, and more particularly to such systems and methods that include hierarchical adaptability and optimization capabilities to operate a hybrid wired and wireless process control and/or automation network while utilizing minimum system resources.
2. Description of Related Art
The current architecture of the wireless networks in various commercial and industrial processing facilities, including hydrocarbon and petrochemical plants, necessitates that most information packets transmitted from the wireless end devices (WEDs) have a single destination, the Central Control Room (CCR). However, the transmissions from the WEDs are passed through several wireless intermediate devices (WIDs) and wireless gateway devices (WGDs), resulting in multiple copies of the same packet arriving at the Central Control Room (CCR) gateway(s). WEDs can transmit to and receive from all other devices, but cannot route to other devices. WIDs transmit to and receive from all other devices, and route to other devices. WGDs transmit to, receive from, and route between other devices, and also conduct high level applications including protocol translation and assignment of paths for source-destination pairs. As used herein, the components WEDs, WIDs and WGDs are also referred to as “nodes.”
Since a typical industrial process requires thousands of instruments, e.g., sensors, valves, diagnostic devices, and the like, that all must transmit information to the CCR, there exists, in the present state of the art, massive contention for access over the wireless bandwidth spectrum in and around the CCR. This contention ultimately results in degradation of the signal throughput and high packet loss rate.
As used herein, “commercial and industrial processing facilities” include chemical plants, hydrocarbon facilities, petrochemical facilities, manufacturing factories, or any facility that uses wireless process automation and/or control.
FIG. 1 is a schematic diagram of hardware interconnectivity for a typical prior art process control network 500 in a commercial and/or industrial processing facility. In FIG. 1, wired connectivity is depicted with solid double-arrow lines between nodes, and wireless connectivity is depicted with dashed double-arrow lines between nodes. Several junction boxes 506 (JBs), and up to several hundred in typical process control systems, are connected, typically by copper or fiber optic wires, to one or more marshalling cabinets 504 in the central control room 501 (CCR). The CCR 501 includes a distributed control system 502 that generally includes at least one processor coupled to a memory for providing functionality necessary for plant automation and/or control. Junction boxes 506 provide data distribution functionality and power (current and voltage) control, and are equipped with requisite power connectivity and a suitable environmental enclosure. The marshalling cabinets 504 provide interconnectivity between several junction boxes 506, and serve as an access point in the CCR 501 for installation of additional JBs, maintenance, testing and service. The JBs can be connected to any wired communication enabled pressure sensor, temperature sensor, pump, valve, tank level gauge, and the like. Typically these end devices can be the same process control device that connects to a WED, the difference being the I/O card of the end device. That is, end devices can be connected to the JBs when they support wired-only connectivity, or both wireless and wired connectivity. For end devices that support wireless-only connectively, a WED must be used. Typically, spare copper or fiber optic wires are provided in a trench between each junction box 506 and the CCR for future growth and expansion. These wire connections can be accessed at the junction boxes 506 and/or surrounding areas. The junction boxes 506 and the plant hardware in wired communication thereto (not shown), along with the marshalling cabinets, for, an independent wired network 509 in typical commercial and industrial processing facilities.
Traditionally, plant and industrial networks have relied on the wire as a means for communications and networking. Wireless communications were introduced within facilities as independent networks. Therefore commercial and industrial processing facilities commonly include a wireless network that is independent of the wired network. The wireless network generally includes a master WGD 510 coupled to the distributed control system 502 via an input/output interface 508. Several WGDs 512 and WIDs 514 are interconnected to each other and to the master WGD 510. The WIDs 514 receive and transmit data from/to the WEDs 516.
In prior art systems as shown in FIG. 1, the wireless network 520 under the control of the master WGD 510 Gateway is completely isolated from the wired network 509 connecting the several junction boxes 506 through the marshalling cabinets 504.
All field devices and subsystems, in the order of thousands, are typically within a relatively small area in a commercial and industrial processing facility, e.g., in a space on the order of about 500 meters by about 300 Meters. The WEDs 516 at the field devices generally broadcast their data, which is received by any and all available WIDs 514 and/or WGDs 512. The WIDs 514 retransmit the data to WGDs 512 and the master WGD 510, and the WGDs 512 retransmit the data to the master WGD 510. Ultimately, packet selection is accomplished with one or more appropriate software and/or firmware modules executable by the master WGD 510, which select the first packet that appears to have accurate data, and subsequent packets containing copes of the same data are discarded. This architecture, with substantial redundancy, is conventionally implemented to ensure that all of the data transmitted from the WEDs 516 is received at the CCR 501 for subsequent action and/or data collection purposes.
The International Society of Automation (ISA) has established a Wireless Systems for Automation Standards Committee (ISA-SP100) tasked with defining wireless connectivity standards. The SP100 wireless standard for process automation systems is applicable to industries such as oil and gas, petrochemical, water/wastewater treatment and manufacturing. The SP100 standard is intended for use in the 2.4 GHz band, with data transfer at speeds up to 250 kilobytes per second within a 300 meter range. SP100 devices have relatively lower data rates and energy requirements than comparable wireless Local Area Networks (LAN), as they are intended to be low-cost devices. Another commonly employed wireless process control and/or automation network has been recently developed as a derivative of the Highway Addressable Remote Transmitter (HART) Communication Foundation protocols, referred to generally as the HART® protocol.
The SP100 protocol specifies different types of communications, categorized as “usage classes,” and increasing in criticality based upon decreasing numerical designation. “Class 0” communications include those categorized as critical for safety applications such as emergency shut-down systems, and are deemed always critical; “Class 1” is for closed-loop regulatory control, often deemed critical; “Class 2” is for closed-loop supervisory control, usually non-critical; “Class 3” is for open-loop control; “Class 4” is for alerting or annunciation; and “Class 5” is for data logging. Certain events, such as alarms, can have different classifications of service depending on the message type.
FIG. 2 is a schematic diagram of a prior art architecture for a wireless process control system 600 of the prior art, e.g., operating under the SP100 standard. In general, devices in an SP100 system are divided into three categories, commonly referred to as “tiers.” Tier 1 includes end devices, such as meters, remote terminal units, valves, sensors, tank level measuring devices, and the like, each of which is connected to a WED 616. Tier 2 includes WIDs 614 and tier 3 includes WGDs 612. As described above, WEDs 616 can transmit to and receive from all other devices, but cannot route to other devices; WIDs 614 transmit to and receive from all other devices, and route to other devices; and WGDs 612 transmit to, receive from, and route between other devices, and also conduct high level applications including protocol translation and assignment of paths for source-destination pairs. In addition, a master wireless gateway device 610 is provided at tier 3, which is coupled to the CCR 601 and controls the ultimate communication of data to and from the DCS 602. Individual nodes are also labeled for further clarity of description and to simplify certain examples provided herein.
Connectivity between WEDs L17 and L13 and WGDs L35 and L31, respectively, is illustrated, although as will be understood by one of ordinary skill in the art, connectivity is typically provided between all WEDs 616 and the master WGD 610 for communication with the DCS 602. A path is the series of nodes commencing with the transmitting node, ending with the receiving node, and including the routing nodes therebetween. A link is a specific coupling within such a path. For example, L17-L293-L292-L36-L35 is a path for the source-destination pair L17-L35, and L292-L36 is one of the links within this path.
Devices in an SP100 wireless system are generally connected in the form of a mesh or star-mesh network. Connection between the various devices is performed through radio communications, for instance as specified by a Carrier Sense Multiple Access with Collision Avoidance (CSMA-CA) protocol or the like, and connections are established at a network layer and a Medium Access Control (MAC) layer.
In existing wireless process control and/or automation systems, every frame transmitted from a WED 616 to the DCS 602 at the CCR 601 is treated the same, regardless of its usage class or criticality. The standards mandate that the transmitted frames reach the DCS 602 within a specified maximum allowable end-to-end time delay and a specified frame error rate (FER). Commonly, all WIDs 614 and WGDs 612 route incoming traffic irrespective of the usage class, and without regard to a frame's status as an original transmission or a retransmission. Multiple paths between WEDs 616 and the master WGD 610 are typically specified in a routing table for increased reliability of data frame transmission and receipt. Retransmission of frames occurs and is requested if the received frame is judged to be erroneous or no acknowledgment is received (i.e., a timeout occurs).
While a large number of paths provide a certain degree of reliability, this topology increases the bandwidth requirements for the wireless spectrum and battery energy usage, and the quantity and/or sophistication level of the requisite hardware. Redundancy of transmission paths also requires additional capital investment in hardware and increased costs for the necessary testing and maintenance of the additional routers. In addition, channel contention often occurs due to high channel utilization, increased latency between the WEDs 616 and CCR 601, and frame blocking. Therefore, diminishing returns result, such that an increase in the number of paths beyond a certain level will not significantly increase the reliability, thereby inefficiently using bandwidth, hardware and battery power. Wireless implementation of the SP100 and the HART® protocols have suffered similar drawbacks including excess battery usage and increased channel contention.
Therefore, there is a significant need to reduce the number of unnecessary transmissions and reduce the number of wireless routers. In addition, a need exists for reliable and adaptable methods and systems to operate a wireless process control and/or automation network while utilizing minimum system resources.
Accordingly, it is an object of the present invention to reduce the overall congestion of wireless traffic in and around the CCR.
It is another object of the present invention to transmit, from one tier to another, data packets that meet optimal performance requirements for each source-destination pair, and maximize the quality of transmitted packets for each source-destination pair.